In separate pots, cook the red lentils, black lentils, and mung beans according to the instructions on their packages. For more flavor, add a few tablespoons of vegetable broth (powder) to the water. If you're short on time and don't mind a mix of textures, you can also cook them together in one pot, but keep a close eye on them as red lentils cook faster than black lentils and mung beans. Once cooked, drain and let them cool slightly.